Transmembrane Transport Flashcards
What are the three major functions of cell membranes
- separate the cell contents from the outside
- separate the contents of different organelles from the rest of the cell
- form a permeability barrier to many biologically important molecules
cells need to take up various substances such as large uncharged polar molecules including
glucose and fructose
cells need to take up various substances such as ions, give some examples
k+ mg2+ , basically any ion lols
cells need to take up various substances such as charged polar molecules including
amino acids, atp, proteins, nucleic acids
what is the typical composition of a cell membrane in terms of the amount of protein compared to the amount of lipid
50% protein, 50% lipid
the membrane of a mitochondria has 75% protein and 25% lipid, why is this
because oxidative proteins are found throughout the membrane for respiration
the membrane of myelin sheath is 25% protein and 75% lipid, why is this
because the nerve cells require insulation
what component of the cell membrane is the key to the ‘selective permeability’ we describe cells as having
it is the protein component of the membrane that is key to the selective permeability to most physiologically important solutes. these are the gateways into cells
membrane proteins have a wide variety of functions, label the following five proteins
channels, transpoters, connexins, receptors and enzymes
what do membrane proteins that are channels do
they allow the ions to be transported across in order to maintain equilibrium
give an example of protein channel
the CFTR protein channel
what does the CFTR protein channel transport across
chloride ions
what does cftr stand for
Cystic fibrosis transmembrane conductance regulator
what do mutations in the CFTR protein channel result in
cystic fibrosis
what do transporter proteins along the cell membrane do
transport substances such as amino acids, sugars and drugs up the concentration gradient
what do connexins do
they interact with the cytoskeleton, extracellular matrix or other cells
what do protein receptors along the cell membrane do
they are involved in endocytosis and or/transmission of signals across the membrane without movement of the ligand
give an example of a protein transporter
ABCB1
what does abcb1, the protein transporter do
it is a drug efflux pump, causes multidrug resistance
give an example of a connexin/integrin membrane protein
Cx26
where is Cx26 found
between cochlear cells
what does Cx26 allow to happen
allows ion flow and so communication between cells
a mutation in the gene of Cx26 results in what
congenital deafness
congenital means?
present from birth
what ion does the Cx26 connexin transport
k+ ions
give an example of a protein receptor
FGFR3 + FGF
if there is a mutation in the protein receptor FGFR3 + FGF, what disease can occur
achondroplasia
what is achondroplasia
a cause of dwarfism
give an example of an enzyme membrane protein
enzyme phospholipase c
phospholipase c which is an example of an enzyme protein on the cell membrane converts phosphatidylinositol into which two substances
ip3 + DAG
once phosphatidylinositol is converted to ip3 + DAG, what does the ip3 allow and what does the DAG allow
ip3 - releases Ca2+ ions from ER and DAG allows PKC activation
how would you describe a channel protein
a continuous pore through a membrane
explain how a channel pore can be selective
it may allow +ve ions through if negatively charged but not allow -ve ions through, or vice versa
in what direction (in terms of concentration gradients) does a channel protein work
it only works down hill - solute moves down its electrochemical gradient to equilibrium
is the bulk flow high or low in a channel protein
high bulk flow
what type of movement occurs across channel proteins and passive transporters/carrier proteins
facilitated diffusion
a carrier transporter/passive transporter can transport molecules that are too large or too polar from both sides of the membrane, how?
a passive transporter has specific solute binding sites alternately exposed on different sides of the membrane
in what direction does a passive transporter/carrier protein work in terms of concentration
works down-hill, down the concentration gradient
what type of flow can occur across a passive transporter
low capacity flow
briefly describe passive transport in three key points
- solute binding sites randomly exposed on either side of mem
- solute binding induces a conformational change, exposing solute to other side of mem
- net flux is dependent on the gradient, and only to equilibrium - obvs doesnt require energy
where are solute binding sites present in active transport
high affinity solute binding site exposed to cytosol
when a solute binds to an active transpoter, what does this induce
solute binding induces atp binding
what is the net flux dependent on in an active transporter and in which direction can the solutes flow
net flux is dependent on atp (primary active pump) and can be uphill - against the conc gradient
*explain this diagram in terms of the electrochemical gradient
electrochemical gradient with no membrane potential
*explain this diagram in terms of the electrochemical gradient
electrochemical gradient with membrane potential negative inside
*explain this diagram in terms of the electrochemical gradient
electrochemical gradient with membrane potential positive inside
which of the three electrochemical gradients is most pertinent to the human plasma membrane
electrochemical gradient with membrane potential negative inside
what creates a powerful electrochemical gradient for Na+ ions
the -ve charge on the inner leaflet phosphatidyl-serine combined with the efflux of sodium ions by the Na+/K+ ATPase pump generates a powerful electrochemical gradient for Na+
some transporters use ATP to provide the energy for solutes to move against the concentration gradient, what other method can generate the energy to pump against the concentration gradient
transport can be driven using the energy from ion gradients - coupled transport
what is coupled transport
coupling of the binding of both the transported solute and the co-transported solute
what provides the energy to transport against the concentration gradient in coupled transport
the free energy released as the co-transported ion moves down its electrochemical gradient can drive the solute up its electrochemical gradient
what is a ion gradient generated by
an atp driven pump
why is coupled transport referred to as secondary active transport
because the ion gradient is generated by an ATP driven pump, so this is secondary active transport
what is a symporter
symporters transport solutes in the same direction
what is an antiporter
antiporters transport solutes in the opposite direction
in a primary active transporter, uphill solute translocation is possible if coupled to what
ATP hydrolysis
in a secondary active transporter, uphill solute translocation is possible if coupled to what
if coupled to the downhill movement of another solute
give an example of a primary active transporter
SERCA - the sacroplasmic/endoplasmic reticulum Ca2+ P-type ATPase
give an example of a secondary active transporter
SGLT1 the sodium/glucose linked transporter
where is the sodium glucose linked transporter found
in the intestinal epithelium
List the three transporters involved in glucose uptake in the epithelium lining the small intestine
- sglt1 symporter
- passive transporter
- na+/k+ ATPase
what is the role of the SGLT1 symporter in glucose uptake
the sglt1 symporter is a na+ driven symporter. glucose is transporter in after the entrance of na+.
what type of active transport occurs at the SGLT1 symporter
secondary active transport
what is the role of the proteins present at the basal domain in epithelial cells of the small intestine
glut2 facilitated diffusion - the downhill transport of glucose
what occurs at the Na+/k+ pump in the epithelial cells
keeps cellular na+ low by pumping Na+ out into the extracellular fluid
what type of transporter is the Na+/k+ atpase pump
a primary active transporter
what is progressive familial intrahepatic cholestasis
Progressive familial intrahepatic cholestasis (PFIC) is a disorder that causes progressive liver disease, which typically leads to liver failure
genetics has identified mutations in transporters resulting in progressive familial intrahepatic cholestasis, list the three transports which may have mutations in them
Atp8b1 - transports phosphatidyl-serine
abcb4- transports phosphatidyl-choline
abcb11 - transports bile salts
give an example of a particle that is internalised by receptor mediated endocytosis
LDL - cholesterol rich low density lipoprotein particles
once the ldl has bound to the ldl binding site of the dl receptor protein on the plasma membrane, what prevents the ldl partciels from entering the cells
the ldl particles are prevented from entering the cells as there is a clathrin coated pit prsent
some people have a genetic mutation resulting in the clathrin pit not being present, what does this result in
hypercholesterolaemia, where the clathrin interaction domain is deleted
what can hypercholesterolaemia result in
a greater risk of atherosclerosis and chd
what is cftr and where is it present
cftr stands for cystic fibrosis transmembrane regulator, it is a cl- channel and is present on the plasma membrane of epithelial cells of the lung, intestine and pancreas
once cl- is transported across the cftr channel protein, what does this induce the flow of
once cl- is transported across, this induces the flow of na+ and water
when na+ and water is transported out of the plasma membrane, what does this reduce
reduces the viscosity of the surface mucous
what happens when the cftr protein is mutated
results in cystic fibrosis. viscous mucous reduces the function of the epithelial cells, causing chronic infection, inflammation and fibrosis
what is fibrosis
the thickening and scarring of connective tissue
mutations of the cftr protein are usually of what type
autosomal recessive
there are usually two types of mutation of cftr, what are these
they either impair the opening of the channel or impair folding of the channel in the er
which mutation is more common, the impaired opening or the impaired folding
the impaired folding is more common,
impairment of the opening of the channel is a result of a genetic mutation in
g551d
impairment of the folding of the channel is a result of the genetic mutation in
f508
focusing on the treatment of cystic fibrosis, what are correctors effective against
they are effective against deltaf508 which impairs the folding of the channel in the er
name a corrector used in the treatment of cystic fibrosis
suberoylanilide hydroxamic acid (saha)
how does suberoylanilide hydroxamic acid work
switches on different folding chaperones which allow f508 to fold
what are potentiators effective against
g551d which impairs the opening of the channel
give an example of a potentiator used in the treatment of cystic fibrosis
ivacaftor
how does ivacaftor work
works by binding directly to the channel and increasing its ability to open
gene therapy currently has ongoing trials, it is likely to be an effective treatment for what part of the body
the lungs
